Diaphragm for loudspeakers

ABSTRACT

A diaphragm for a loudspeaker made of foamed plastic or like material, in which the diaphragm has a decreased thickness at its central portion to which a voice coil is attached.

United States Patent 1 1 1111 3,708,035 Sotome 14 1 Jan. 2, 1973 [54] DIAPHRAGM FOR LOUDSPEAKERS [58] Field of Search ..l8 1/32 R, BIG. 1, 31 R 75 Invent lliromi Sotom l-lam ts h, 1 9r Japan ama u s l [56] References Cited [73] Assignee: Nippon Gakkl Seizo Kabushiki UNITED STATES PATENTS 5 Hamamatsu'sh" shzuoka' 1,832,832 11/1931 Nagelvoor! ..1s1/s2 R 1,872,081 8/1932 l-lawley ...1s1/32 R 22 i Feb 4, 1971 2,905,260 9/1959 Williams ...l8l/32 R 3,172,498 3/l965 Gorlke ..l8l/32 R [21] Appl. No.: 112,784

Primary Examiner-Stephen J. Tomsky Related Application Data Attorney-Stevens, Davis, Miller & Mosher [63] Continuation-impart of Ser. No. 803,822, March 3, 1969, Pat. No. 3,586,l21. 57 ABSTRACT 3 Foreign Application p i it Data A diaphragm for a loudspeaker made of foamed plastic or like material, in which the diaphragm has a Nov. 30, 1967 Japan ..42/100056 decreased thickness at i central portion to hi h a voice coil is attached. [52] U.S. Cl. ..l8l/32 R, l8l/DlG. 1 [51] Int. Cl ..Gl0k 13/00, H041" 7/00 2 Claims, 8 Drawing Figures PATENTED 2 I975 3.7 08 O35 sum 2 BF 2 mvmon H/KDH/ rare/v5 ATTORNEYS DIAPHRAGM FOR LOUDSIEAKERS The present application is a continuatiOn-in-part of application Ser. No. 803,822, filed Mar. 3, 1969, now U. S. Pat. No. 3,586,121, issued June 22,1971.

BACKGROUND OF THE INVENTION The present invention relates to a diaphragm for a loudspeaker made of foamed plastic or like material.

Heretofore a number of types of diaphragm made of foamed plastic, such as foamed polystyrene or like material, have been proposed. FIGS. 1 A, B, C, D and E illustrate some examples of such diaphragm. FIG. I A shows a diaphragm made of a flat plate la having uniform thickness of foamed plastic material such as foamed polystyrene and having a voice coil 2a attached to its central portion. FIG. 1 B shows a diaphragm made of a flat plate 1b having a thickness increasing stepwise toward its central portion to which a voice coil 2b is attached. FIG. 1 C shows a diaphragm made of a flat plate 1c having a thickness increasing gradually toward its central portion to which a voice coil 2c is attached. FIG. 1 D shows a diaphragm made ofa plate 1d having uniform thickness which is formed in a cone having an apex portion to which a voice coil 2d is attached. FIG. 1 E shows a diaphragm made of a flat plate 1e which is formed at its central area in a gradually curved conical form, to which a voice coil 2e is attached.

These diaphragms can faithfully reporduce low frequency sounds and their frequency characteristics in the'low frequency range depend on piston motion or on overall bending (fundamental single bending) motion of the diaphragm. However, in the medium or high frequency ranges, the diaphragms tend to produce divided vibrations, resulting in peaks and dips in their frequency characteristics. Consequently, a smooth frequency characteristic such as in a conventional cone-type loudspeaker using a cone paper diaphragm cannot be obtained in these diaphragms. Furthermore, these diaphragms have relatively increased mass at the central portion, so that they cannot satisfactorily reproduce higher frequency sounds. I

SUMMARY OF THE INVENTION It is an Object of the present invention to provide a diaphragm for a loudspeaker made of foamed plastic or like material which can reproduceeffectivelyhigh frequency sounds as well as low frequency sounds.

It is another Object of the present invention to provide a diaphragm for a loudspeaker made of foamed plastic or like material in which a flat or smooth frequency characteristic curve can be obtained throughout the whole range from low frequency to high frequency.

In accordance with the present invention, there is provided a diaphragm for a loudspeaker made of foamed plastic or like material in which the diaphragm has a decreased thickness at its central portion to which a voice coil is attached.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 A, B, C, D and E are sections showing examples of conventional loudspeaker diaphragms;

FIGS. 2, 3 and 4 are sectional views showing several embodiments of the diaphragm according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 2, 3 and 4 illustrate some embodiments of the in that it lacks rigidity at the central portion so that deep dips may occur in the frequency characteristic in its low frequency range.

FIG. 3 shows a second and most preferred embodiment of the present invention in which a diaphragm is made of a flat plate 3b which is formed in a gradually curved conical shape so as to gradually increase its rigidity at its central area. In this central area the plate 3b gradually decreases its thickness toward the central portion 4b to which a voice coil 5b is attached, thereby decreasing mass of effective vibrating area which contributes to the vibration of the diaphragm at high frequency range. This diaphragm is also fixed at its circumference by means 7b.

FIG. 4 shows a third embodiment of the present invention, in which a diaphragm is made of a flat plate 3c of foamed plastic or like material which is formed in a gradually curved conical shape at its central area, as in' area where angle of inclinationis relatively small, said thick part 6 serving to increase the rigidity of the plate to improve the frequency characteristics in the low frequency range. The plate 30 gradually decreases its thickness from the thick part 6 toward a central portion 40 where the angle of inclination is increased, to which a voice coil 5 is attached. Means 7c are used to fixedly hold the edge of the diaphragm along its circumference. In such a construction, the plate has a relatively high rigidity in the central portion owing to its conical shape although the thickness is decreased'toward the central portion, so that characteristic in the low frequency range is not adversely affected by the decrease of the thickness. Furthermore, while the level in medium frequency range generally tends to be increased by forming the plate in the conical shape, excessiveincrease in level is prevented owing to the increase Of vibrating mass in the medium frequency range by the thick part 6. Thus a relatively flat or smooth characteristic curve can be obtained through 'low frequency sound to high frequency sound.

The following table shows two examples of the diaphragm constructed in accordance with the present invention.

Thickness at Of course, the thickness may be properly determined, depending on the size of the diaphragm, the

material of the diaphragm or the desired characteristics.

It will be understood from the above description that in accordance with the present invention, sounds can be effectively reproduced throughout whole range from low frequency to high frequency with a flat or smooth frequency characteristic, by a diaphragm made of foamed plastic or like material which could not heretofore give a flat frequency characteristic.

What is claimed is:

1. In a diaphragm for a loudspeaker, said diaphragm comprising a member the major portion of which is substantially planar and of substantially uniform thickness foamed plastic and said diaphragm having a voice coil attached thereto, the improvement which comprises providing in the central portion of said member an indentation of curved conical shape, the angle of inclination of the walls of said conical indentation with respect to the diaphragm axis gradually increasing as the apex of the conical shape is approached, the walls of said curved conical indentation gradually decreasing in thickness towards said apex, said voice coil being attached to said apex, and means fixedly securingsaid diaphragm at the circumference thereof. 

1. In a diaphragm for a loudspeaker, said diaphragm comprising a member the major portion of which is substantially planar and of substantially uniform thickness foamed plastic and said diaphragm having a voice coil attached thereto, the improvement which comprises providing in the central portion of said member an indentation of curved conical shape, the angle of inclination of the walls of said conical indentation with respect to thE diaphragm axis gradually increasing as the apex of the conical shape is approached, the walls of said curved conical indentation gradually decreasing in thickness towards said apex, said voice coil being attached to said apex, and means fixedly securing said diaphragm at the circumference thereof.
 2. A diaphragm according to claim 1, wherein the substantially planar portion of said member has a radial width approximately equal to two-thirds of the radial distance from said diaphragm axis to the exterior edge of said member and said indentation of curved conical shape has a maximum radial width of approximately one-third of said distance from said diaphragm axis to said edge of said member. 